LEM’s new ARU range of Rogowski Coils measure current up to 300000 A AC with accuracy class 0.5 according to IEC 61869-10 without the need for additional components are being launched at this years SPS. Their new HMSR series of miniature current sensors are also being launched. They can handle overload current bursts of up to 20 kA such as those that occur in photovoltaics applications while still providing a reinforced isolation
ARU Rogowski coils for easy outdoor installation with Accuracy Class 0.5
The Rogowski coils range to measure current up to 300,000 A AC with accuracy class 0.5 are being launched by LEM at SPS. The ARU range achieves IEC 61869-10 class 0.5 without the need for additional components such as resistors or potentiometers to calibrate the coil, which can drift over time. The range benefits from ‘Perfect Loop’ technology, a unique patented coil clasp that eliminates the inaccuracy caused by sensitivity to the position of the conductor inside the loop. This technology provides an innovative, robust and fast ‘Twist and Click’ closure.
Compared with the previous LEM Rogowski coils ART, the ARU range can be installed outdoors as the models are compliant with UV, water, dust and ice resistance standards. The range has also ruggedized material to be durable in extreme environments (wide operating temperature range up to -40 to +80oC). Moreover, an internal shield is provided to protect against external fields, improving accuracy and optimising performance for small current measurements.
The ARU series provides the same ease of installation as existing split-core current transformers, but with the benefits of being thinner and more flexible.
Whatever the chosen dimension – 70, 125, 175, 250 & 300-mm diameter for the aperture – the ARU can be mounted very quickly by simply clipping on to the cable to be measured. Contact with the cable is not necessary, while the ARU models ensure a high level of safety as well as provide a high rated insulation voltage (1000 V Cat III PD2 – reinforced).
The ARU range allows the coil disconnection to be detected by a security seal passed through a specially designed slot, making it useful when used with a metering device. They can be used in applications requiring a protection degree up to IP 68.
The models include an accuracy class 0.5 and complete the LEM product portfolio for the AC current measurement. LEM is dedicated to future distribution network applications and offers innovative and high-quality solutions for measuring electrical parameters into the Smart Grid.
The Smart Grid is in the middle of a radical transition, as millions of electric vehicles hit the roads and Terawatts of renewable energy capacity are installed in our grids. Smarter equipment is needed for the Smart Grid, providing reliable integration of intermittent renewable energies and distributed energy resources. LEM improves the grid by measuring electrical parameters, allowing control rooms to automate, monitor remotely and share real-time equipment data. Typical applications are Distribution Automation for Fault Detection, Isolation & Restoration, Grid Monitoring (e.g. Intelligent substations), Protection & Safety, Distribution Transformer Monitoring, Distribution Automation for Voltage Control and Power Quality.
The ARU series current sensors are CE marked and conformed to the IEC 61869 standard series, as well as being covered by LEM’s five-year warranty.
Surface mounted high isolated current sensors range with an included current conductor
LEM has expanded its range of miniature, integrated circuit sensors range for AC and DC isolated-current measurement with the introduction of the HMSR series. Despite their small size, the components can handle overload current bursts of up to 20 kA (8-20 us surge test profile), such as those that occur in photovoltaics applications while still providing a reinforced isolation. Products in the series are designed to measure currents of up to 2.5 times their nominal ratings of 6 A, 8 A, 10 A, 15 A, 20 A or 30 A.
Packaged as SO16 surface-mount devices with a height of just 6 mm, the sensors can be mounted directly onto a printed circuit board in the same process as other board-level components. This helps to reduce manufacturing costs and decrease the overall footprint, vital for space-constrained applications. As a result, HMSR sensors can be readily built into small form-factor intelligent power modules (IPMs).
The HMSR series uses a proprietary Open Loop Hall effect ASIC associated with a unique low-resistance primary conductor to minimise power losses allowing direct current measurement and high transient overload currents to pass without damage. The use of a ferrite for the magnetic element is a key factor in achieving a high frequency bandwidth of 270 kHz (-3dB) and to provide good rejection against external fields. The unique mechanical design for the sensor leads to creepage and clearance distances of 8 mm using materials with comparative tracking index (CTI) of 600, the whole to meet reinforced isolation according to the IEC 60950-1 standard.
An integrated EEPROM is used for programmable internal temperature compensation to counter offset and gain drifts and perform gain stress compensation. These measures ensure high-performance overall accuracy over the full range of temperature, from -40 to +125°C with a typical value of 0.5 % of IPN for the HMSR 20-SMS model, a significant improvement over the previous generation. The HMSR series achieves a shorter response time: 2 µs typical.
The output signal from the sensor is an analogue voltage. The sensitivity levels are determined by the models. For the 5V power-supply versions, the output voltage is of 800 mV @ IPN. As standard, devices in the HMSR range provide two different over-current detection (OCD) warning levels on 2 dedicated pins: one threshold is set during manufacturing at 2.93 x IPN; the other can be adjusted by the user using external resistors.
The HMSR is ideal for demanding applications such as photovoltaics, which require high insulation levels together with stringent controls on price and product size. Similarly, the small size benefits applications such as drives for white-goods, window shutters and air-conditioning systems. The HMSR’s ability to support high frequency currents thanks to the use of a ferrite as magnetic circuit with low losses suits drives that operate with higher switching frequencies.
Additionally, the low cost of the HMSR series makes the device competitive against shunts with the added benefits of high insulation and OCD features.
The HMSR series conform to the latest industrial standards and devices are covered by LEM’s five-year warranty.